It's a reason why I don't really trust signal. They don't want to be recompiled by 3rd party. You must either trust them (or the app stores, which isn't better) or go through the hassle of figuring out how to build it yourself.
With fdroid i trust 1 party, by downloading random binaries I have to trust hundreds.
https://github.com/signalapp/Signal-Android/blob/main/reprod...
Why? The official one can be backdoored and with a gag order you would never hear about it
Not trusting signal's build and then turning around and trusting some third party build seems strange. The official build probably has more eyes on it, and signal has more reputation to lose.
I'd start here if I were you: https://protonvpn.com/support/wireguard-configurations